(Press-News.org) Washington, D.C. (October 5, 2010) -- Carbon nanotubes -- long, hollow cylinders of carbon billionths of a meter in diameter -- have many potential uses in nanotechnology, optics, electronics, and many other fields. The exact properties of nanotubes depend on their structure, and scientists as yet have little control over that structure, which is determined during the initial formation -- or growth -- of the nanotubes. In fact, says chemical engineer and materials scientist Eray Aydil of the University of Minnesota, "we do not know precisely how the nanotubes grow."
In a paper in the American Institute of Physics' Journal of Applied Physics, Aydil, professor of chemical engineering and materials science and the Ronald L. and Janet A. Christenson Chair in Renewable Energy, and his colleagues shed new light on the process. In particular, the researchers examined the influence of hydrogen gas.
"Carbon nanotubes grow from a metal catalyst particle that is immersed in a gas like methane," Aydil explains. "Sometimes hydrogen gas is also added and it was found that a little bit of hydrogen helps to grow carbon nanotubes with nice straight walls and with few defects. However, too much hydrogen addition gives fibers with thick walls, instead of nanotubes, or no growth at all."
To understand why, Aydil and colleagues used transmission electron microscopy and other methods to systematically image and characterize the effects of increasing concentrations of hydrogen. "It turns out that the iron metal catalysts turn to iron carbide by reacting with the carbon in methane. Iron carbide is a hard material that is not easily deformed, and carbon nanotubes grown from such catalysts tend to have nice straight walls," he says.
Adding more hydrogen to the mix causes iron carbide to turn into iron -- which is more malleable and ductile, and "deforms into shapes that give rise to more fiber-like structures rather than hollow carbon nanotubes," he says. At higher concentrations, hydrogen etches the forming carbon nanotubes, "and growth stops all together. It is the interaction of the hydrogen with the catalysts and its effect on the catalyst's structure that controls the carbon nanotube structure."
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The article, "Effect of Hydrogen on Catalyst Nanoparticles in Carbon Nanotube Growth" by Eray S. Aydil, Michael J. Behr, Elizabeth A. Gaulding and K. Andre Mkhoyan (University of Minnesota) appears in the Journal of Applied Physics. http://link.aip.org/link/japiau/v108/i5/p053303/s1
ABOUT JOURNAL OF APPLIED PHYSICS
Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics; content is published online daily, collected into two online and printed issues per month (24 issues per year). The journal publishes articles that emphasize understanding of the physics underlying modern technology, but distinguished from technology on the one side and pure physics on the other. See: http://jap.aip.org/
ABOUT AIP
The American Institute of Physics is a federation of 10 physical science societies representing more than 135,000 scientists, engineers, and educators and is one of the world's largest publishers of scientific information in the physical sciences. Offering partnership solutions for scientific societies and for similar organizations in science and engineering, AIP is a leader in the field of electronic publishing of scholarly journals. AIP publishes 12 journals (some of which are the most highly cited in their respective fields), two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Its online publishing platform Scitation hosts nearly two million articles from more than 185 scholarly journals and other publications of 28 learned society publishers.
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For Immediate Release - (October 5, 2010) –Toronto's Centre for Addiction and Mental Health (CAMH) has been selected as one of seven adult field trial sites in North America and the only site in Canada to test proposed diagnostic criteria for the American Psychiatric Association's (APA) fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM). Used by health professionals around the world, DSM is the manual that provides descriptions, symptoms and other criteria for diagnosing mental disorders. CAMH is participating in field trials to help assess ...
A research team from the University of British Columbia and the Child & Family Research Institute (CFRI) at BC Children's Hospital has identified the role of a type of T cell in type 1 diabetes that may lead to new treatment options for young patients.
Also known as juvenile diabetes, type 1 diabetes is an autoimmune disease primarily affecting children and young adults. In patients with type 1 diabetes, the body attacks itself by destroying insulin-producing cells in the pancreas that regulate glucose, or blood sugar.
Led by Rusung Tan, a Pathology professor in the ...
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dx.doi.org/10.1126/science.opms.r1000097.
The article will be posted at this URL address the evening of 7 October 2010.
The American Association for the Advancement of Science (AAAS) is the world’s largest general scientific society, and publisher of the journal, Science (www.sciencemag.org) as well as Science Translational Medicine (www.sciencetranslationalmedicine.org) and Science Signaling (www.sciencesignaling.org). AAAS was founded in 1848, and includes some 262 affiliated ...
Spanish and Scottish researchers have added wool fibres to the clay material used to make bricks and combined these with an alginate, a natural polymer extracted from seaweed. The result is bricks that are stronger and more environmentally-friendly, according to the study published recently in the journal Construction and Building Materials.
"The objective was to produce bricks reinforced with wool and to obtain a composite that was more sustainable, non-toxic, using abundant local materials, and that would mechanically improve the bricks' strength", Carmen Galán and ...
Pioneering new research by archaeologists at the University of York suggests that Neanderthals belied their primitive reputation and had a deep seated sense of compassion.
A team from the University's Department of Archaeology took on the 'unique challenge' of charting the development of compassion in early humans.
The researchers examined archaeological evidence for the way emotions began to emerge in our ancestors six million years ago and then developed from earliest times to more recent humans such as Neanderthals and modern people like ourselves. The research by ...
Allergies occur when the defence mechanisms of the immune system malfunction and misread normal substances entering the body as invading pathogens. Antibodies are part of our biochemical arsenal for combating viruses, bacteria, parasites and other alien substances, but during an allergic reaction the antibody, known as IgE, is directed against usually harmless substances such as grass pollen, nuts, pets or eggs. Asthma and allergies are chronic diseases that reduce quality of life and pose an economic burden on society. New parents have therefore previously been asked if ...
Light drinking during pregnancy does not harm a young child's behavioural or intellectual development, reveals research published online in the Journal of Epidemiology and Community Health.
A previous study of 3 year olds drew similar conclusions, but the authors wanted to rule out possible delayed "sleeper" effects in older children.
They used data from the Millennium Cohort Study - a large study tracking the long term health of children born in the UK - drawing on a representative sample of 11,513 children born between September 2000 and January 2002.
Participants' ...
The provision of made-to-order drugs ("specials") in primary care is expensive, often unnecessary, and associated with legal pitfalls, says the Drug and Therapeutics Bulletin (DTB).
It calls for a major overhaul of the practice, in a review of the evidence in this month's issue.
Bespoke drugs or "specials" are medicines made specifically to meet the needs of individual patients, so may be prepared in formulations and strengths which differ from those of standard licensed medicines.
They might be prescribed, for example, when a patient can't or won't swallow tablets ...
A persistently noisy workplace more than doubles an employee's risk of serious heart disease, suggests research published online in Occupational and Environmental Medicine.
Young male smokers seemed to be particularly at risk, the findings showed.
The researchers base their findings on a nationally representative sample of more than 6,000 employees, aged from 20 upwards, who had been part of the US National Health and Nutrition Examination Survey (NHANES) between 1999 and 2004.
This involved detailed household interviews, to include lifestyle and occupational health, ...
Therapeutic antibodies can be an efficient alternative when common drugs do not work anymore. However, antibodies obtained from blood of animals such as mice could not be used: The human immune system recognizes them as foreign and rejects them. In an international cooperation, scientists from the Helmholtz Centre for Infection Research (HZI) in Braunschweig, Germany have now succeeded in developing a promising approach to solve this problem; with the help of human stem cells they generated mice with a human immune system, which were then vaccinated to produce human monoclonal ...
